Transition to the Mid-Paleozoic
The Early Silurian saw recovery from the Late Ordovician mass extinction.
Most taxa rediversified in an evolutionary radiation that led to a refilling of vacated niches:
Trilobites became less conspicuous.
Brachiopods became much more conspicuous.
Bivalve mollusks invaded fresh water.
Planktonic graptolites diversified spectacularly.
Many new swimming predators evolved during the Silurian and Devonian.
Early Silurian graptolite,
Cotton Formation, Cottons Hill Quarry, New South Wales, Australia. ►
Image courtesy of The Virtual Fossil Museum, www.fossilmuseum.net.